Indirect Effects of a Fungal Entomopathogen, Lecanicillium Lecanii (Hypocreales: Clavicipitaceae), on a Coffee Agroecosystem Ant Community Author(S): A
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Indirect Effects of a Fungal Entomopathogen, Lecanicillium lecanii (Hypocreales: Clavicipitaceae), on a Coffee Agroecosystem Ant Community Author(s): A. J. MacDonald, D. Jackson, and K. Zemenick Source: Environmental Entomology, 42(4):658-667. 2013. Published By: Entomological Society of America URL: http://www.bioone.org/doi/full/10.1603/EN12287 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. COMMUNITY &ECOSYSTEM ECOLOGY Indirect Effects of a Fungal Entomopathogen, Lecanicillium lecanii (Hypocreales: Clavicipitaceae), on a Coffee Agroecosystem Ant Community 1,2 3 3,4 A. J. MACDONALD, D. JACKSON, AND K. ZEMENICK Environ. Entomol. 42(4): 658Ð667 (2013); DOI: http://dx.doi.org/10.1603/EN12287 ABSTRACT Fungal entomopathogens are widely distributed across natural and managed systems, with numerous host species and likely a wide range of community impacts. While the potential for fungal pathogens to provide biological control has been explored in some detail, less is known about their community interactions. Here we investigate the effects of fungal epizootics of the entomopatho- gen Lecanicillium lecanii (Zimmerman) on a keystone mutualism between Azteca instabilis (F. Smith), a dominant arboreal ant, and the green coffee scale (Coccus viridis Green), as well as broader impacts on a coffee agroecosystem ant community. We hypothesized that seasonal epizootics cause shifts in the foraging ranges of A. instabilis as the ants adapt to the loss of the resource. We further hypothesized that the magnitude of these shifts depends on the availability of alternate resources located in neighboring shade trees. To test these hypotheses, we induced an epizootic in experimental sites, which were compared with control sites. Surveys of ant activity were undertaken pre- and post- epizootic. We found a decrease in foraging activity of A. instabilis and increase in activity of other ant species in the experimental sites post-epizootic. The decrease in abundance of A. instabilis foragers was greater on plants in which an epizootic was induced than in other plants. This relationship was modiÞed by shade tree density where higher shade tree density was associated with larger decreases in A. intabilis foraging activity in coffee plants. These results demonstrate the potential for fungal entomopathogens to inßuence the structure and diversity of ecological communities. KEY WORDS Lecanicillium lecanii, fungal epizootic, Azteca instabilis, self-organization, disturbance Fungal entomopathogens have been widely studied as cesses that structure communities is an important av- biological control agents in numerous systems and enue of research. against numerous different pests (Shah and Pell 2003, Community structure and patterns of diversity have Scholte et al. 2005, Pell et al. 2010). While the direct been demonstrated to result from numerous processes effects of the use of fungal biocontrol on pest species and underlying biotic and abiotic conditions (Paine have been of primary interest to date, the important 1966, 1969; Connell 1978; Hastings 1988; Caley and St. roles these organisms play as interacting members of John 1996; Chesson 2000; Hansen 2000; Bascompte and ecological communities in complex food webs are Jordano 2007; Perfecto and Vandermeer 2008). Of poorly understood and little studied (Meyling and particular importance in our study system, spatial pat- Hajek 2010). Population regulation and host-pathogen tern has emerged as an important variable in the study interactions are implicit in the treatment of fungal of the distribution of biodiversity at numerous scales entomopathogens simply as agents of biological con- (Ritchie 2010). The spatial distribution of a population trol, yet indirect effects with important implications or community throughout a landscape has often been for the structure and diversity of communities are assumed to result from underlying habitat structure omitted. Therefore, addressing the role of ento- mopathogenic fungi in complex interactions and pro- (Forman and Gordon 1987, Turner et al. 1990). How- ever, there may be other factors contributing to ob- 1 School of Natural Resources and Environment, University of served spatial patterns, particularly when considering Michigan, 3531 Dana Bldg., 440 Church St., Ann Arbor, MI 48109. relatively uniform landscapes (Skarpe 1991, Rohani et 2 Corresponding author: Department of Ecology, Evolution, and al. 1997, Bascompte and Sole´ 1998, Alados et al. 2007, Marine Biology, UC Santa Barbara, 2107 Noble Hall, University of Scanlon et al. 2007, Sole 2007). For example, observed California, Santa Barbara, CA 93106 (e-mail: andrew.macdonald@ ´ lifesci.ucsb.edu). patterns and distributions in relatively uniform eco- 3 Department of Ecology and Evolutionary Biology, University of systems, such as managed agroecosystems, may be the Michigan, 2077 Kraus Natural Science, 830 North University, Ann result of endogenous self-organization arising from Arbor, MI 48109. 4 Ecology Graduate Group, UC Davis, Department of Entomology, species interactions rather than underlying habitat 320 Briggs Hall, One Shields Av., Davis, CA 95616. variables (Pascual et al. 2002, Sole´ and Bascompte 0046-225X/13/0658Ð0667$04.00/0 ᭧ 2013 Entomological Society of America August 2013 MACDONALD ET AL.: ENTOMOPATHOGENS IN AN AGROECOSYSTEM ANT COMMUNITY 659 2006, Perfecto and Vandermeer 2008, Rietkerk and insects? 2) How does habitat complexity, in this case van de Koppel 2008, Vandermeer et al. 2008). proximity of other shade trees to A. instabilis nest- Here we address the indirect effects of a fungal sites, inßuence the response of A. instabilis to a local entomopathogen, Lecanicillium lecanii (Zimmer- epizootic? and 3) How is the arboreal foraging ant man), and its ecological role, in promoting spatial community affected by the response of A. instabilis, self-organization and pattern formation. In our study the dominant ant competitor, to a local epizootic? We system, a tropical coffee agroecosystem, a keystone predicted that A. instabilis would abandon coffee arboreal-nesting ant, Azteca instabilis (F. Smith), bushes with large populations of infected scale insects forms a mutualism with the green coffee scale, Coccus and respond either by expanding their foraging activ- viridis (Green). The ant protects the scale from pred- ity to coffee bushes in the periphery of previously ators and parasites, and the scale provides a nutrient tended bushes, or by switching their foraging activity rich secretion in return (Vandermeer et al. 2002). The to shade trees, and the alternate resources therein, in ant colonies nest in shade trees that are planted in an close proximity to nests. Furthermore, we predicted approximately uniform distribution throughout the that if A. instabilis foraging activity shifted to shade farm, tending the scale insects that live on the coffee trees, it would impact the arboreal foraging ant com- plants below. The spatial distribution of the A. insta- munity by promoting expansion of competitively sub- bilis ant nests, which occur in clusters whose size dominant arboreal foraging ant activity into coffee distribution can be described with a fat tail distribu- bushes previously tended by A. instabilis, thereby pro- tion, is thought to arise through a process of self- viding access to previously unavailable resources (i.e., organization characterized by local expansion of clus- low density scale insect populations). In contrast, we ters counteracted by density-dependent mortality predicted that if A. instabilis were to expand foraging (Perfecto and Vandermeer 2008, Vandermeer et al. to peripheral coffee bushes, it would displace foraging 2008). A fungal entomopathogen, L. lecanii, attacks activity of other arboreal foraging ants, forcing them the local concentrations of scale insects that are as- to seek alternative resources. sociated with the clusters of ant nests, greatly reducing the scale populations and possibly causing density- Materials and Methods dependent control of the A. instabilis colonies (Jack- son et al. 2009), although other factors have been The study site is located at Finca Irlanda, a 280 ha, proposed (Vandermeer et al. 2008). organic coffee farm in the Soconusco region of We hypothesize that seasonal epizootics of L. lecanii Chiapas, Mexico (15Њ 11Ј N, 92Њ 20Ј W). The farm is a periodically disrupt ant foraging activity, causing dy- commercial polyculture (Moguel and Toledo 1999), namic shifts in the foraging ranges of A. instabilis as the with coffee bushes growing beneath shade trees that ants attempt to adapt to the loss of a primary food have been planted uniformly throughout the farm.